Once again during 1861 the country was in serious danger of war with England, and the action of President Lincoln at this time proved not only that he had the will to be just, even when his own people were against him, but had the skill to gain real advantage from what seemed very like defeat. One of the earliest and most serious tasks of the Government had been to blockade the southern ports, in order to prevent supplies from foreign countries reaching the southern people, especially the southern armies. Considering the great length of coast to be patrolled, and the small size of the navy at the commencement of the struggle, this was done with wonderful quickness, and proved in the main effective, though occasionally a rebel boat managed to slip in or out without being discovered and fired upon by the ships on guard.

In November Captain Charles Wilkes learned that Ex-Senators J. M. Mason and John Slidell, two prominent Confederates bound on an important mission to Europe, had succeeded in reaching Cuba, and from there had taken passage for England on the British mail steamer Trent. He stopped the Trent and took Mason and Slidell prisoners, afterward allowing the steamer to proceed on her way. The affair caused intense excitement both in England and in the United States, and England began instant preparations for war. Lord Lyons, the British Minister at Washington, was instructed to demand the release of the prisoners and a suitable apology within one week, and if this were refused, to close his legation and come home. It was fortunate that Lord Lyons and Mr. Seward were close personal friends, and could, in spite of the excitement of both countries, discuss the matter calmly and without anger. Their conferences were brought to an end by Mr. Lincoln's decision to give up the prisoners. In the North their capture had been greeted with extravagant joy. Newspapers rang with praises of Captain Wilkes; his act was officially approved by the Secretary of the Navy, and the House of Representatives passed a resolution thanking him for his "brave, adroit, and patriotic conduct." In the face of all this it must have been hard indeed for Mr. Lincoln to order that Mason and Slidell be given up; but though he shared the first impulse of rejoicing, he soon became convinced that this must be done. War with England must certainly be avoided; and Captain Wilkes, by allowing the Trent to proceed on her voyage, instead of bringing her into port with the prisoners, had put it out of the power of his Government to prove, under international law, that the capture was justified. Besides all else, the President's quick mind saw, what others failed to note, that by giving up the prisoners as England demanded, the United States would really gain an important diplomatic victory. For many years England had claimed the right to stop and search vessels at sea when she had reason to believe they carried men or goods hostile to her interests. The United States denied the right, and yet this was exactly what Captain Wilkes had done in stopping the Trent. By giving up the prisoners the United States would thus force England to admit that her own claim had been unjust, and bind her in future to respect the rights of other ships at sea. Excited American feeling was grievously disappointed, and harsh criticism of the Administration for thus yielding to a foreign country was not wanting; but American good sense soon saw the justice of the point taken and the wisdom of Mr. Lincoln's course.